Analog signal storage and readout have a variety of uses and are accomplished by a variety of means as exemplified by phonographic and magnetic tape recording and playback devices. Typically, output from readout devices is in the form of an electrical signal which may be used, e.g., to drive a loudspeaker or an optical display device.
While phonographic and magnetic tape devices are commercially well established, alternate technologies have been developed for specialized applications. For example, U.S. Pat. No. 3,508,222 (issued Apr. 21, 1970 in the name of A. H. Bobeck) discloses a device for analog signal storage and readout utilizing patterned electrodes which are deposited on a sheet of magnetic material.
In the context of the invention, a class of materials is relevant which in some respects is similar to the class of magnetic materials. Members of this class, known as ferroelectric materials, exhibit electric polarization in two preferred antiparallel directions and permit the simultaneous presence of regions of either polarization. Furthermore, some such materials have different optical properties associated with the two polarization states, a feature which has been utilized in various electro-optical devices. For example, U.S. Pat. Nos. 3,953,109 (issued Apr. 27, 1976 in the name of A. Kumada) and 3,936,146 (issued Feb. 3, 1976 in the names of A. Kumada et al) disclose devices in which a ferroelectric material is used for light control. Optical properties of ferroelectric materials are also utilized as disclosed in U.S. Pat. No. 3,701,122 (issued Oct. 24, 1972 in the names of J. E. Geusic et al) for readout of digital shift registers in which digital data are represented by ferroelectric domains.
While readout from digital ferroelectric devices has been demonstrated in principle, analog signal storage and readout have remained unexplored.